This invention relates generally to medical equipment systems of the type which apply therapeutic radiation to the internal tissues of the body of a living being following insertion of a source of radiation into a cavity within the body, and more particularly, to an applicator system which affords the facility to ascertain the suitability of a proposed location and position for a source of the therapeutic radiation within the body cavity prior to exposure of the living being to the radiation.
It is now well known to use hollow applicator tubes which contain radioactive sources for treatment of cancerous tissue, such as cancerous cervical tissue, within body cavities. In one early and widely used arrangement designed for the treatment by radiation of cervical cancer, hollow applicator tubes, or colpostats, are provided with radiation sources fixed therewithin. Metallic shields are provided for the purposes of directing the emission and shaping the field of exposure to the emitted radiation. It is a significant problem with this known arrangement that the patient's exposure to radiation commences immediately upon insertion of the applicator tubes, and prior to the adjustment of the location and position of the source, such that healthy tissue is disadvantageously exposed to the radiation.
Improvements to the early system permit emplacement of the hollow applicator tubes with the metallic shields attached thereto, and then afterloading of the radiation source into the applicator tubes. Such pre-placement of the hollow applicator tubes permits the user to predetermine, to a limited extent, the positioning of the applicator tube before the radiation source is inserted. Thus, the strength of the radiation capsule in each position may be chosen to optimize radiation dose. This arrangement includes the fixed metallic shields of the early system. The improved arrangement has attained significant acceptance, and is commercially available.
One drawback of the improved system is that when computerized tomography (CT) is used to scan the region to ensure proper placement of the applicator elements, the metallic shields cause CT image distortions called "streak artifacts." These distortions make discernment of the exact position of tissues adjacent to the applicator tubes very difficult.
It has been proposed to eliminate all metal shields on the applicator tube(s) and to use instead a non-metallic dummy (or test) source so as to obtain clear CT scan imaging of the tissues surrounding the placed applicator tubes, and when checking the pre-placement of the applicator ensemble in the vagina and uterus adjacent to the cervix. However, the prior art has not proposed a solution to the replacement of the removed exterior shielding. The prior art structure is not optimal because excessive radiation emission can adversely affect healthy tissues which may be in the vicinity of the applicator and which are not scheduled for irradiation.
Even when clear CT scans are made using a nominally CT-transparent test source, the applicator tubes may be seen to be properly located relative to the surrounding tissue, but it may be desirable to adjust the direction and emission pattern of the emitted radiation. Such adjustment, however, cannot be achieved using the known fixed shields. Even if the shields were adjustable, removal of the applicator tubes would be required, followed by reinsertion thereof and subsequent confirmation of location and position via further CT imaging. Thus, it would be desirable to be able to alter the shield geometry in response to the CT scan image, and to do so without requiring removal and reinsertion of the applicator tubes.
In addition to the foregoing, since more than one applicator tube and radiation source carrier are commonly used, it is very important that the proper radiation source carrier and applicator tube be paired to avoid error and incorrect treatment. This is especially critical since the usual practice is that the applicator tube placement and test imaging are performed in the hospital imager location, and the actual radiation source carriers may be inserted elsewhere, such as in the patient's room, since a long period of irradiation would otherwise encumber space in the operating clinic or test equipment areas.
It is, therefore, an object of this invention to provide a radiation applicator system which does not distort CT scan imaging.
It is another object of this invention to provide a radiation applicator system which does not distort CT scan imaging and which has adjustable shielding to attenuate radiation emitted by a contained radiation source.
It is additionally an object to provide a radiation applicator system having a combination of applicator tubes and radiation sources, with controllable shielding, wherein loading of a radiation source in a pre-placed applicator tube is facilitated, after the location of the applicator tube within the body cavity has been verified by imaging.
It is also an object of this invention to provide a radiation applicator system which permits alteration of the geometry of the shielding around the radiation source after the applicator tube(s) have been placed within the body and imaging of the region has been performed, to enable shaping of the field of exposure to the radiation and to ensure that a proper dose of radiation is administered to the selected tissue, while simultaneously blocking radiation emitted towards nearby non-selected tissue regions.
It is a further object of this invention to provide a radiation applicator system having applicator tubes which are fabricated from a material which does not degrade CT scanning and which can be manufactured sufficiently inexpensively so as to be disposable.
It is additionally an object of this invention to provide a radiation applicator system wherein a dummy source for standard x-ray simulation can be provided in addition to a dummy source which does not degrade CT images for CT scanning, to permit the resulting CT images to be of a quality sufficient to enable precise determination of the position of the actual radiation source vis-a-vis surrounding tissue structures.
Another object of the invention is to provide a radiation applicator system wherein CT images produced using a dummy source contain a visual indicator to assist in determining the exact position of the actual radiation source with respect to surrounding body tissues when the actual source replaces the dummy source.
It is yet a further object of this invention to provide a radiation applicator system having a combination of an applicator tube(s) together with a test or dummy source(s) which accurately represents the dimensions of the actual radiation source to be placed within the applicator tube, to facilitate placement of the radiation source within the body cavity and to provide clear test images, whereby proper placement and an estimate of the forthcoming radiation treatment efficacy can readily be ascertained.
It is also another object of this invention to provide a radiation applicator system constructed to have an applicator tube having a hollow portion having an inner diameter which accommodates a selectable one of either an actual radiation source, and appropriate shielding, or a dummy surrogate source which is used to predetermine the irradiation source location before final placement and treatment begins.
It is still another object of this invention to provide a radiation applicator system having multiple applicator tubes and means for identifying sets of applicator tubes and respective source carrier assemblies so that the proper radiation source and associated shields are inserted therein and inadvertent interchange of radioactive source carrier assemblies is prevented.